This disclosure relates to an airfoil having a leading edge cooling trench and impingement cooling.
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.
In the pursuit of ever higher efficiencies, gas turbine manufacturers have long relied on high and higher turbine inlet temperatures to provide boosts to overall engine performance. In typical modern engine applications the gas path temperatures within the turbine exceed the melting point of the component constituent materials. Due to this, dedicated cooling air is extracted from the compressor and used to cool the gas path components in the turbine incurring significant cycle penalties. Further, variable cycle engines, which utilize bypass ratio changes during operation, are being developed to increase engine overall fuel consumption. With features such as variable fan nozzles or variable turbine vanes, the bypass ratio of the engine can be shifted between high power situations to part power or cruise operation.
A primary mechanism in which to cool turbine gas path components is to utilize a series of in-wall channels which passes cooling air which is typically several hundreds to thousands of degrees colder than the gas path. In one type of cooling configuration, for very high heat load applications, impingement cooling is typically employed. These impingement holes are typically integrally formed within the ceramic core of the turbine blade and due to the nature of manufacturing of the ceramic core must lie parallel to the pull plane of the core die in a manner in which the pull action of the die release is still enabled. The limitation of implementation with inclusion to a cast core process imposes that impingement is limited in scope to this region negating its use widely across the airfoil unless secondary internal baffled devices are used.
Typically, the leading edge region of a turbine airfoil experiences the highest heat load of the entire part. The heat transfer coefficients located at the stagnation point of the airfoil are typically 1.5-2 times the values seen on the downstream portions of the airfoil. As a result, airfoil cooling configurations are typically setup to produce the highest cooling effectiveness in this location, which in turn consumes one of the largest amounts of air on the part. In another type of cooling configuration, film troughs or trenches are typically utilized to improve the film effectiveness of showerhead film. The trench creates a pocket of cool air that shields the leading edge from the hot gas path. The trench is typically machined after holes are drilled.